The present invention relates to a curable rubber composition and the use thereof, and more particularly to a curable composition for providing a hard rubber having a high dynamic modulus of elasticity with improved processability and workability and a radial tire using the hard rubber as a bead filler.
In general, a radial tire has a structure in which, as shown in FIG. 1, cords of carcass ply 1 are arranged parallel to each other in the radial direction of the tire, that is, transversely to the equator plane of the tire, the carcass ply 1 being turned up at its both ends outwardly from the inside of bead wire 2 disposed concentrically with the tire on both sides thereof, and a bead filler rubber 3 is provided inside the turned-up end portion of the carcass ply, the bead filler rubber 3 extending from a location just above the bead wire 2 toward the side wall of the tire. In the tire of such a structure, there might be created a gap of rigidity due to tire structure in the neighborhood of the top of the turned-up end portion 1a of the carcass ply at bead 6, resulting in occurrence of cracks in the circumferential direction of the tire along the gap.
In order to prevent the occurrence of such a damage at the bead, it has been proposed to use a hard rubber having a high dynamic modulus of elasticity of more than 300 kg./cm..sup.2 as the bead filler rubber 3. However, production of a cured rubber having such a high dynamic modulus of elasticity in a factory has involved many problems on workability and processability. In a conventional process for producing a hard rubber having a high elasticity, it has been a common practice to use a large amount of thermosetting resin, a large amount of a curing agent, a large amount of a curing accelerator or a combination thereof in order to increase the density of crosslinkage. However, such a process has a problem of rubber scorching due to voluminous heat generation at the time of milling a rubber composition by a Banbury mixer, or of impairing the tackiness of rubber due to blooming of the curing agent upon processing. Also, because of high viscosity of the rubber composition, there would be produced excessive load upon milling or extrusion.
Accordingly, it is an object of the present invention to provide a curable composition having improved processability and workability.
A further object of the present invention is to provide a curable composition capable of giving a hard rubber having a high dynamic modulus of elasticity.
Another object of the present invention is to provide a radial tire using the hard rubber as the bead filler rubber.
These and other objects of the invention will become apparent from the description hereinafter.